In general, in a friction drive apparatus such as a disk drive system, a material such as rubber which has a considerably large friction coefficient is used to cover at least one of two opposing contact surfaces, so that a sufficient contact pressure acts between these two surfaces, thereby transmitting the rotational force through a sufficient friction force. However, when a friction drive apparatus is not used for a long period of time, a rubber surface which has been in tight contact with the opposing contact surface becomes locally recessed, since the rubber surface deforms over time. When the friction drive apparatus is rotated again under this condition, the local recess results in mechanical vibration. In particular, in electronic equipnent such as a cassette tape recorder which is greatly affected by mechanical vibration, the deformation over time described above has the effect of degrading wow and flutter characteristic. In addition, the deformation causes noise and vibration.
On the other hand, when a friction wheel which is biased to apply a predetermined contact pressure is directly coupled to a motor shaft, the biasing force is affected by the self-weight of the motor. The contact pressure between the friction wheel and the flywheel varies in accordance with an orientation of the tape recorder. In this manner, the self-weight of the motor affects and degrades precision and reliability.